JP3039949B2 - Optical fiber manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[Field of Industrial Application] The present invention relates to a method for producing an optical fiber having a carbon coating formed on the surface thereof. By limiting the raw material compounds, an optical fiber having excellent hydrogen resistance and mechanical strength can be obtained. It is intended to be. [Prior Art] When a silica-based optical fiber comes into contact with hydrogen, absorption loss due to molecular vibration of hydrogen molecules diffused into the fiber increases, and further, P ₂ O ₅ and Ge contained as dopants are used.
Since O ₂ , B ₂ O _3, etc. react with hydrogen and are taken into the fiber glass as OH groups, there is a problem that transmission loss due to absorption of OH groups increases. To cope with such adverse effects, a method of filling a liquid composition having a hydrogen absorbing ability into an optical cable (Japanese Patent Application No.
No. 251808) is considered, but the effect is insufficient, and the structure becomes complicated, which is economically problematic. In order to solve such problems, it has recently been announced that a carbon coating can be formed on the surface of an optical fiber by chemical vapor deposition (hereinafter abbreviated as CVD), thereby improving the hydrogen resistance of the optical fiber. Have been. In this method, a bare optical fiber spun by a spinning furnace is inserted into a CVD reactor, and a raw material gas composed of a hydrocarbon compound or the like is supplied. This is a method of forming a coating. By the way, in the method for producing an optical fiber, when a hydrocarbon compound is used as a raw material gas during the thermal decomposition reaction,
Various by-products are generated in addition to the carbon coating. These by-products are hydrogen radicals, protons, hydrogen molecules and the like (hereinafter collectively referred to as hydrogen radicals and the like). When these by-products are diffused into the optical fiber, the strength of the optical fiber decreases and Silanol groups (Si-OH), which cause an increase in transmission loss, are generated. As a method of preventing the generation of silanol groups by suppressing the generation of this by-product, a method using a halogenated hydrocarbon as a raw material gas has already been proposed by the present applicant. In this method, halogen radicals, halogen ions and halogen molecules generated by thermal decomposition of halogenated hydrocarbons (hereinafter collectively referred to as halogen radicals and the like) are used to capture hydrogen radicals and the like that cause the formation of silanol groups. Into hydrogen halide. [Problems to be Solved by the Invention] However, in the above-described method, when the amount of generated hydrogen radicals and the like is larger than the amount of generated halogen radicals and the like, there is an inconvenience that generation of silanol groups cannot be eliminated. Further, not all halogen radicals and the like generated react with the hydrogen radicals and the like, and there is a dissatisfaction that the action of suppressing silanol group formation is not yet sufficient. The present invention has been made in order to solve the above-mentioned problems, and an object of the present invention is to provide a method for obtaining a high-strength optical fiber having excellent hydrogen resistance by suppressing the generation of silanol groups. . Means for Solving the Problems In order to solve the above problems, the invention described in claim 1 provides a method for manufacturing an optical fiber, wherein a raw material gas is thermally decomposed to form a carbon coating on the surface of the bare optical fiber. The raw material gas is a mixed gas of benzene and chlorine gas, and the ratio B / A of the chemical equivalent A of hydrogen in benzene to the chemical equivalent B of chlorine in chlorine gas is 0.3 to 1.4.

[Action]

Since hydrogen radicals and the like generated by thermal decomposition of benzene are captured by chlorine radicals and the like generated by thermal decomposition of chlorine and converted into hydrogen chloride, generation of silanol groups is suppressed. Further, by determining the chemical equivalents of hydrogen and chlorine, hydrogen radicals can be captured without excess or deficiency. Hereinafter, the present invention will be described in detail. FIG. 1 shows an example of an optical fiber manufacturing apparatus suitably used for the optical fiber manufacturing method of the present invention. In FIG. 1, reference numeral 1 denotes a bare optical fiber. The bare optical fiber 1 is obtained by heating and spinning an optical fiber preform (not shown) in an optical fiber spinning furnace 2.
Is spun and supplied into a CVD reactor 3 provided below the optical fiber spinning furnace 2. The CVD reactor 3 is for forming a carbon coating on the surface of the bare optical fiber 1 spun in the upper optical fiber spinning furnace 2 by a CVD method.
The reaction tube 4 includes a generally cylindrical reaction tube 4 that allows the reaction to proceed, and a heating element 5 that heats the reaction tube 4. A source gas supply pipe 6 for supplying a raw material compound into the reaction tube 4 is attached to an upper portion of the reaction tube 4, and an exhaust pipe 7 for exhausting unreacted gas and the like is attached to a lower portion thereof. The mixing device 11 as shown in FIGS. 2 and 3 is connected to the raw material gas supply pipe 6. The mixing device 11 is formed of a bifurcated pipe, supplies benzene, chlorine gas, and an inert gas as a carrier gas from branch pipes 11a and 11b, respectively. It can be discharged from the pipe 11c. By connecting such a mixing device 11 to the source gas supply pipe 6, the mixing ratio of benzene and chlorine gas of the source gas can be freely and easily adjusted. Further, gas seal mechanisms 8 for sealing the reaction tube 4 are connected to the upper and lower portions of the reaction tube 4, respectively. The reaction tube 4 and the heating element 5 for heating the reaction tube 4 can be appropriately selected depending on the heating temperature and the like.
An induction CVD reactor, an infrared CVD reactor, or the like can be used, and a heating element that generates plasma using high frequency or microwave to ion-decompose the raw material compound can also be used. Further, a resin liquid coating device 9 is provided below the CVD reactor 3.
And a curing device 10 are provided continuously, so that a protective coating layer can be formed on the carbon coating formed in the CVD reactor 3. The following steps are used to manufacture an optical fiber using the above manufacturing apparatus in accordance with the manufacturing method of the present invention. The optical fiber preform is heated and spun in the optical fiber spinning furnace 2 and the CVD provided in the lower stage of the optical fiber spinning furnace 2.
Inserted into the reaction furnace 3, the resin liquid coating device 9, and the curing device 10,
Supply is performed so as to travel at a predetermined linear speed on these central axes. Next, the heating element 5 is heated to heat the inside of the reaction tube 4 to a predetermined temperature, and a source gas is supplied from the source gas supply tube 6 into the reaction tube 4. The raw material gas is passed through a mixing device 11 as shown in FIGS. 2 and 3, so that benzene and chlorine gas are mixed at a predetermined concentration in the inert gas. The supply rate of the raw material gas is appropriately selected depending on the types of benzene and chlorine gas and their mixing ratio, the heating temperature of the CVD reactor 3, and the like, but is preferably about 0.2 to 1.0 / min. The mixing ratio of benzene to chlorine gas is preferably such that the ratio B / A of the chemical equivalent A of hydrogen in benzene to the chemical equivalent B of chlorine in chlorine gas is 0.3 to 1.4. If the equivalent ratio B / A is less than 0.3, chlorine is insufficient, and hydrogen radicals and the like generated when benzene is thermally decomposed cannot be completely captured to suppress the production of silanol groups.
On the other hand, if the equivalent ratio B / A is more than 1.4, the chlorine concentration during the reaction becomes too high, and the adhesion of the carbon coating to the surface of the bare optical fiber 1 is undesirably reduced. The temperature in the reaction tube 4 can be appropriately selected depending on the type of the raw material gas, the spinning speed, and the like, but may be any temperature that is sufficient for the thermal decomposition of benzene, and is preferably about 500 to 1400 ° C. If the heating temperature is lower than 500 ° C, the thermal decomposition of benzene does not proceed, and if it is higher than 1400 ° C, a large amount of by-product soot is generated and the structure of the carbon coating formed on the surface of the bare optical fiber 1 is reduced. It is not preferable because it becomes close to a graphite structure and sufficient hydrogen resistance cannot be obtained. In order to prevent the generation of soot as a by-product, the heating temperature is desirably set to be slightly lower than the thermal decomposition temperature of the raw material compound. The optical fiber bare wire 1 on which the carbon coating is formed in this way is introduced into a resin liquid coating device 9 provided in a lower stage,
Next, it is inserted into a curing device 10 for curing the resin liquid. The bare optical fiber 1 inserted into the resin liquid coating device 9 is coated with an ultraviolet curable resin liquid or a thermosetting resin liquid for forming a protective coating layer, and then cured appropriately for the applied resin liquid. The protective coating layer is formed by being cured in the curing device 10 having conditions. As described above, when a mixed gas of benzene and chlorine gas is used as a source gas, hydrogen radicals and the like are trapped by chlorine radicals and the like, and a silanol group that causes a decrease in the strength of the optical fiber is not generated. Can be obtained. Further, since the carbon coating obtained by thermally decomposing these source gases has a dense structure, the obtained optical fiber also has excellent hydrogen resistance. In this example, a single carbon coating was formed on the surface of the bare optical fiber 1. However, the number of carbon coatings formed on the surface of the bare optical fiber 1 is not limited to this, and two or more carbon coatings may be formed. May be formed continuously. Further, in this example, a single protective coating layer is formed on the carbon coating, but the number of protective coating layers is not limited to this, and a plurality of protective coating layers may be formed. Example A resistance CVD reactor having a quartz tube reaction tube was attached to the lower stage of a spinning furnace for spinning an optical fiber bare wire from an optical fiber preform. Next, a single-mode optical fiber preform having an outer diameter of 30 mm and having a core portion impregnated with GeO ₂ as a dopant was placed in the spinning furnace. This optical fiber preform was heated to 2000 ° C. and spun into a single mode optical fiber having an outer diameter of 125 μm at a spinning speed of 60 m / min. 1300 ° C inside the resistance CVD reactor
Heated. Benzene diluted with helium gas to about 10 vol% and chlorine gas were mixed by a mixing device. The mixing ratio was varied as shown in Table 1 by changing the equivalent ratio B / A between the chemical equivalent A of hydrogen in benzene and the chemical equivalent B of chlorine in chlorine gas. The mixed gas was supplied at a flow rate of 5 / min into the reaction tube while keeping the temperature of the mixed gas constant at 30 ° C. to form a carbon coating on the bare optical fiber surface. By-products and unreacted substances were removed from the exhaust pipe at an exhaust pressure of -6 mmHg. Further, a urethane acrylate resin liquid (Young's modulus 70 kg / mm ² , elongation 60%) is sealed in the resin coating die spot, and the optical fiber on which the carbon coating is formed in the above process is inserted into the resin spot, and the surface thereof is exposed. After applying an ultraviolet-curable resin solution to the substrate, the resin solution was cured by irradiating an ultraviolet lamp to produce an optical fiber having an outer diameter of about 250 μm. (Test Example 1) Each of the optical fibers obtained in the above example was 1 km long and 1 mm in diameter.
The bundle was placed in a 50 mm bundle, and left in a pressure vessel for evaluating hydrogen resistance at a hydrogen partial pressure of 1 atm and a temperature of 80 ° C. for 48 hours. Wavelength after this 1.
The increase in transmission loss (dB / km) at 24 μm was measured. The results are shown in Table 1. (Test Example 2) 25 optical fibers obtained in the above example were put together,
A tensile test was performed under the conditions of a gauge length of 3 m, a strain rate of 10% / min, 23 ° C. and 50% RH, and a Weibull plot of the breaking probability and the tensile strength was performed, and the tensile strength at a 50% breaking probability was measured. The results are shown in Table 1. From the above results, Example 1 according to the manufacturing method of the present invention.
It was confirmed that each of the optical fibers Nos. To 6 exhibited high mechanical strength and excellent hydrogen resistance. And it was confirmed that an optical fiber having particularly excellent mechanical strength and hydrogen resistance was obtained when the ratio B / A of the chemical equivalent of hydrogen and chlorine in the mixed gas was in the range of 0.3 to 1.4. [Effect of the Invention] As described above, the method for manufacturing an optical fiber according to the present invention is directed to a method for manufacturing an optical fiber in which a raw material gas is thermally decomposed to form a carbon coating on a bare optical fiber surface. It is a mixed gas of benzene and chlorine gas, and the chemical equivalent A of hydrogen in benzene and the chemical equivalent B in chlorine gas
And the ratio B / A of 0.3 to 1.4, the formation of silanol groups in the formed carbon coating is suppressed, and a mechanical strength is high, and an optical fiber having excellent hydrogen resistance is obtained. be able to.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an example of an optical fiber manufacturing apparatus suitably used in the optical fiber manufacturing method of the present invention, and FIGS. 2 and 3 each show a mixing apparatus for mixing benzene and chlorine gas. FIG. 2 is a schematic configuration diagram showing an embodiment of the device. 1 .... bare optical fiber.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Keiji Ohashi 1440, Mukurosaki, Sakura City, Chiba Prefecture Inside the Sakura Plant of Fujikura Electric Wire Co., Ltd. (72) Inventor Shinji Araki 1440 Mutsuzaki, Sakura City, Chiba Prefecture Fujikura Electric Wire & Cable Company Sakura Plant (72) Inventor Hideo Suzuki 1440 Mutsuzaki, Sakura City, Chiba Pref. Fujikura Electric Cable Co., Ltd.Sakura Plant (72) Inventor Nobuyuki Yoshizawa 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (56) References JP-A-2-263743 (JP, A) JP-A-3-153549 (JP, A) JP-A-2-302343 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name ) C03C 25/02

Claims (1)

(57) [Claims] 1. A method for manufacturing an optical fiber, wherein a raw material gas is thermally decomposed to form a carbon coating on a bare optical fiber surface, wherein the raw material gas is a mixed gas of benzene and chlorine gas, A method for producing an optical fiber, wherein the ratio B / A of the chemical equivalent A to the chemical equivalent B of chlorine in chlorine gas is 0.3 to 1.4.